load cf7 modules the same way cf7 does. better detection of contact-form-7-modules.

git-svn-id: https://plugins.svn.wordpress.org/contact-form-7-multi-step-module/trunk@789134 b8457f37-d9ea-0310-8a92-e5e31aec5664
also detect contact-form-7-3rd-party-integration/hidden.php

git-svn-id: https://plugins.svn.wordpress.org/contact-form-7-multi-step-module/trunk@789137 b8457f37-d9ea-0310-8a92-e5e31aec5664